Search Results (25)

Due to the high-precision angle measurement performance, the monopulse technique plays a key role in fields such as remote sensing and space surveillance. The accuracy of monopulse angle measurement depends on the received amplitude and phase information, which is sensitive to the polarization component. Previous research has demonstrated that the performance of monopulse radar equipped with a parabolic antenna suffers from the cross-polarization component. However, it is not clear whether phased arrays (PAs) with higher degrees of freedom will also be affected by the cross-polarization component, and the parameter tolerance for performance degradation remains uncertain. In this paper, we establish a mathematical model of monopulse angle measurement in PA radar, which provides a comprehensive consideration of the cross-polarization component. Then, the received amplitude and phase patterns of PA radar are analyzed, and the theoretical angle errors caused by the cross-polarization jamming are derived. The experiments are conducted based on the measured amplitude-phase patterns of both co-polarization and cross-polarization. Experimental results are consistent with the theoretical analysis: the angle errors caused by cross-polarization jamming can reach half of the beamwidth in both azimuth and elevation dimensions, provided that the power of the cross-polarization and co-polarization components at the receiver is equal. Full article

In this paper, we propose and prove an innovative radar antenna concept suitable for collision avoidance (CA) systems installed onboard small, unmanned aircraft (UA). The proposed architecture provides 360° monopulse coverage around the host platform, enabling the detection and accurate position estimation of airborne, non-cooperative intruders using lightweight, low-profile antennas. These antennas can be manufactured using low-cost 3D printing techniques and are easily integrated into the UA airframe without compromising airworthiness. We present a Detect and Avoid (DAA) concept of operations (ConOps) aligned with the SESAR U-space ConOps, Edition 4. In this ConOps, the Remain Well Clear (RWC) and CA functions are treated separately: RWC is the responsibility of ground-based U-space services, while CA is implemented as an airborne safety net using onboard equipment. Based on this framework, we derive operation-centric design requirements and propose an antenna architecture based on a fixed circular array of sector waveguides. This solution overcomes key limitations of existing radar antennas for UAS CA systems by providing a wider field of view, higher power handling, and reduced mechanical complexity and cost. We prove the proposed concept through a combination of simulations and measurements conducted in an anechoic chamber using a 24 GHz prototype. Full article

The Laser Powder-Bed Fusion Additive Manufacturing (LPBF AM) technique is evaluated for the manufacturing of fully metallic monolithic microwave components. To validate the manufacturing technique, a difference pattern array of 4 × 4 horn antennas is designed to operate at mm-Wave frequencies. The antenna is based on H-plane power dividers and a complex structure to obtain a difference radiation pattern by rotating twisted sections in two different orientations. The prototype is manufactured with a monolithic piece of aluminum alloy AlSi10Mg, providing a lightweight single structure that includes both radiating elements and a feeding network consisting of twisters and power dividers in a waveguide. The prototype was experimentally evaluated in an anechoic chamber and the near-field planar acquisition range, obtaining good agreement with full-wave simulations within an operational bandwidth from 34 to 36 GHz. The results demonstrate that the LPBF AM technique is a suitable candidate to produce challenging monolithic metal-only microwave components in the ${\mathrm{K}}_{\mathrm{a}}$-band, such as monopulse antennas. Full article

Angle estimation for low-altitude targets above the sea surface is a challenging problem due to multipath interference from surface reflection signals, and various approaches have been proposed. This paper proposes a matrix pencil method with multiple apertures. The matrix pencil method effectively responds to dynamic scenarios because it performs better when using a single snapshot than other methods. Also, employing multiple apertures is more economical than using one large aperture. Therefore, we propose a computationally efficient approach using this method and structures. The proposed two-stage MP method incrementally improves the resolution in two stages: in stage 1, we extract the denoised signals at each aperture level, and in stage 2, we further improve the resolution with those signals. In comparison with the angular resolution defined by the half-power beamwidth (HPBW) of a uniform linear array (ULA) antenna with an equivalent number of arrays, the proposed method demonstrated a superior resolution of less than 0.087 of the HPBW at a high signal-to-noise ratio (SNR) of 40 dB, and less than 0.31 of it even at a relatively low SNR of 15 dB, based on 90% of the resolving probability. For the multipath problem, the proposed scheme has the advantage of not requiring prior geometric information, and its performance is demonstrated through simulations to be better than the adaptive beamforming method and the composite monopulse method. Full article

This article describes a new design for the sum-channel, circularly-polarized, radiating patch element of a multimode patch-monopole monopulse feed. Such feeds are suitable for the prime-focus illumination of a deep symmetric reflector. A relatively simple and compact feed design allows for a compact single-mirror antenna with monopulse tracking. The feed is about a wavelength in diameter, also making it suitable for illuminating smaller antennas, for example, in LEO-satellite ground (client) stations. The design applies a slotted circular patch as a circularly-polarized sum-channel element. The design variables are optimized mainly for the sum-channel aperture illumination efficiency in an S-band satellite ground station. After a few cut-and-try iterations, the final feed prototype was produced and measured. In addition to an additional degree of freedom in the geometry and potentially easier fabrication, the new sum-channel radiating-element shape allows for a slightly better monopulse channel isolation, and a higher radiation-pattern symmetry compared to the previous design. Full article

With increasing interest in the W-band, there is growing focus on parabolic reflector antennas that are known for efficiently inducing high-gain radiation characteristics. There is particular focus on parabolic antennas with diverse defocus-fed applications, including monopulse tracking, multi-beam formation using multiple feeds, and aperture-shared antennas for multi-band operation. Thus, a new simplified method is presented in this paper to analyze the radiation characteristics of defocus-fed parabolic antennas. The presented method is based on the discrete division of a parabolic reflector surface and considers only simplified wave propagation theory and the effect of the scalar function pattern from the feeder. Additionally, array theory is exclusively applied for the analysis of radiation characteristics. Therefore, the presented method uses a very simplified formula to calculate the radiation characteristics of a defocused parabolic reflector antenna. The performance of the presented method was evaluated by comparing the results with commercial EM tools. The results of the analysis confirm the applicability of the presented method for the analysis of defocus-fed parabolic antennas. Full article

When constructing a wireless communication network, the line of sight of radio waves is limited by the terrain features in a ground communication network. Also, satellite communication networks face capacity limitations and are vulnerable to jamming. Aviation communication networks can solve the above-mentioned problems. To construct seamless aviation communication networks, fast counterpart location estimation and efficient beam steering performance are essential. Among various techniques used for searching the counterpart’s location, the monopulse technique has the advantage of quickly estimating the location through a simplified procedure. However, the nonlinear characteristics of the monopulse ratio curve, which are inevitably caused by the general antenna beam shape, both limit the location estimation range and reduce the estimated location accuracy. To overcome these limitations, a method that improves the estimation accuracy and extends the range by correcting the sum and difference patterns using the beamforming technique of active phased array antennas was proposed. An antenna system model suitable for aviation communication networks was presented, and the proposed model was experimentally proven to be effective. An average angle error of 0.021° was observed in the estimation of the accuracy of the antenna location. Full article

A one-dimensional mono-pulse microstrip antenna plays an important role in target detection, tracking, recognition and imaging. However, feeding and coupling are the main reasons for the large size of the mono-pulse antenna, which is not conducive to miniaturization and integration. A miniaturized mono-pulse antenna is proposed to reduce the size and improve the integration in antenna design. The proposed antenna has a more compact size and good isolation, with a well-maintained radiation pattern and zero depth. The antenna unit size is 0.19 λ₀ × 0.19 λ₀ × 0.006 λ₀. The overall antenna size is 78 mm × 78 mm × 1.48 mm (0.63 λ₀ × 0.63 λ₀ × 0.0012 λ₀). In this communication, a general decoupling feeding network for two-element microstrip array antennas is also designed. Experiment validations confirm that the operating frequency of the designed antenna system is at 2.45 GHz with a gain of 5.54 dBi. The return loss of the sum and difference ports is 16.14 dB and 15.2 dB, respectively. The isolation of the ports is 36.6 dB. The proposed miniaturized mono-pulse antenna is approximately 64% smaller in size compared to previous versions. Full article

In this paper, a novel concept of a three-dimensional full metal system including a Dual-Mode Converter (DMC) network integrated with a high-gain Conical Horn Antenna (CHA) is presented. This system is designed for 5G millimeter wave applications requiring monopulse operation at K-band ($37.5–39\mathrm{GHz}$). The DMC integrates two mode converters. They excite either the $T{E}_{11}{}^{cir}$ or the $T{E}_{01}{}^{cir}$ modes of the circular waveguide of the CHA. The input of the mode converters is the $T{E}_{10}{}^{rec}$ mode of two independent WR-28 standard rectangular waveguide ports. By integrating the DMC with the CHA, the whole system, called a Dual-Mode Conical Horn Antenna (DM-CHA), is formed, radiating the sum ($\Sigma$) and difference ($\mathsf{\Delta }$) patterns associated to the monopulse operation. To adequately prevent the propagation of higher order modes and mode mutual coupling, this integration procedure is carefully designed and fabricated. To prove the performance of the design, the DMC network was fabricated using subtractive manufacturing by Computer Numerical Control (CNC) technology. The CHA was fabricated using additive manufacturing by Direct Metal Laser Sintering (DLMS) technology. Finally, the simulation and measurement results were exhaustively compared, including return loss, isolation, radiation pattern, and gain of the full DM-CHA structure. It is noteworthy that this system provided up to $\pm 11°$ per beam in the angular of arrival detection to support the high data rate operation for 5G satellite communications in the millimeter-wave band. Full article

Blinking jamming is an active self-screening technique performed by at least two aircraft to tackle monopulse radars and all complexity related thereto. Nowadays, the technique can be performed with digital radiofrequency memories (DRFMs), which are cumbersome, complex, expensive, need a dedicated compartment and antenna, and introduce spurs in the signals. In this paper, we propose an alternative to the implementation of blinking jamming with DRFMs, namely with reconfigurable metasurfaces. By covering the aircraft parts that most contribute to the radar cross-section (RCS), reconfigurable metasurfaces can interchangeably absorb or amplify impinging waves, making the aircraft ‘blink’ from the radar perspective. To validate the feasibility, simulations accounting for realistic phenomena are conducted. It is seen that, if the aircraft RCS can be varied in a ratio of 10:1, either with absorptive or power-amplifying metasurfaces, a performance similar to that of the DRFM is achieved. Furthermore, a ratio of 2:1 is sufficient to make the radar antenna system movements exceed the angular range of the formation. We also anticipate our work to be a starting point for completely new ways of countering radars, e.g., with countless small drones performing passive or active stand-off blinking jamming. Full article

To ensure high-reliability communication in healthcare networks, this paper presents a smart gateway system that includes an angle-of-arrival (AOA) estimation and a beam steering function for a small circular antenna array. To form a beam toward healthcare sensors, the proposed antenna estimates the direction of the sensors utilizing the radio-frequency-based interferometric monopulse technique. The fabricated antenna was assessed based on the measurements of complex directivity and the over-the-air (OTA) testing in Rice propagation environments using a two-dimensional fading emulator. The measurement results reveal that the accuracy of the AOA estimation agrees well with that of the analytical data obtained through the Monte Carlo simulation. This antenna is embedded with a beam steering function employing phased array technology, which can form a beam spaced at 45° intervals. The ability of full-azimuth beam steering with regard to the proposed antenna was evaluated by beam propagation experiments using a human phantom in an indoor environment. The received signal of the proposed antenna with beam steering increases more than that of a conventional dipole antenna, confirming that the developed antenna has great potential of achieving high-reliability communication in a healthcare network. Full article

Presented in this paper is a conceptual design by computer simulation of a monopulse reflector antenna with dual-circularly polarized sum patterns and linearly polarized azimuth and elevation difference patterns, which can be called a semi-dual polarized antenna. The proposed antenna consists of a five-element monopulse feed and a prime-focus parabolic reflector. The novelty of the proposed antenna is a monopulse feed consisting of a dual-circularly polarized square waveguide sum channel radiator and linearly polarized rectangular waveguide azimuth and elevation difference channel radiators. The separation of dual circular polarization is realized by a septum polarizer. The difference pattern is obtained by feeding two rectangular waveguides in opposite directions using a coaxial probe. The proposed monopulse feed geometry requires only two power combiners for a monopulse comparator network while providing dual-polarized performance comparable to the full dual-polarized sum and difference channel monopulse scheme. The concept of the proposed antenna is shown in a conceptual design by computer simulation. The monopulse feed is designed first, and then combined with a parabolic reflector. The designed monopulse reflector antenna operates at 14.5–16.0 GHz, and shows excellent sum and difference pattern characteristics: 36.1–36.7 dBc sum channel directivity with 0.65 dB boresight axial ratio and 32.6–32.9 dBi difference channel directivity with 1.56–1.66° crossover angle. Full article

This paper presents a design for a monopulse reflector antenna with asymmetric beamwidths for radar applications at the Ku band. The proposed design features a rectangular waveguide monopulse feed and a truncated parabolic reflector. An array of four open-ended rectangular waveguides were employed to realize a compact monopulse feed. The reflector is cut in the H plane of the feed producing a wider beam in the azimuth plane. This type of pattern is useful in applications such as projectile tracking and airport surveillance. The design parameters for optimum performances are chosen at all stages of the design. The design and analysis have been carried out using the commercial simulation tool CST Studio Suite 2022. The directivity of the sum, elevation difference and azimuth difference channels of the reflector antenna are 32.1, 28.1, and 26.4 dB at 14 GHz; 30.9, 29, and 27.3 dB at 15 GHz; 31.7, 29.6, and 27.6 dB at 16 GHz; 31.6, 29.9, and 27.8 dB at 17 GHz. Full article

Traditional monopulse radar cannot resolve two closely spaced targets present in one resolution cell (range and Doppler) by means of the monopulse ratio. This study presents a closed-form solution to resolve the directions of arrival of two unresolved targets using a single snapshot of four independent channels in phase comparison monopulse radar. If both targets have the same elevation or same azimuth direction, the proposed scheme cannot estimate their directions. To estimate the direction of such targets, an extra antenna is required. The impact of input noise power, the targets’ direction, and phase difference of the targets’ signal on the accuracy of angle estimation are also explained. The numerical simulation result validates the effectiveness of the presented scheme. Full article

This paper proposes a novel metasurface-based monopulse antenna. A multimode pyramidal horn with four ports is selected as the feed of the proposed monopulse antenna. The 3-dB couplers and the optimized waveguide phase shifters are employed to design the monopulse comparator. In order to obtain good sum and difference beams performance, metasurfaces are mounted on a bowl structure to radiate the electromagnetic wave from the sub-reflector. An experimental prototype of the proposed design has been fabricated and measured at Ku-band. The measured results show that the gain ratio between the sum and difference beams is 2.8 dB and 3.7 dB, respectively. More importantly, the peak gain of the sum beam at 16 GHz is 27.1 dB, without considering the loss of the comparator, with a corresponding aperture efficiency of about 41.4%. This indicates that the proposed structure is beneficial for improving the sum and difference beams performance of the monopulse antenna, which is suitable for tracking platforms. Full article